A file server is a computer that provides file service relating to the organization of information on storage devices, such as disks. The file server includes a storage operating system that implements a file system to logically organize the information as a hierarchical structure of directories and files on the disks.
The storage devices in a file server environment are typically disk drives organized as a disk array, wherein each disk is a self-contained rotating magnetic media storage device. A disk array further comprises disk array controllers which manage the physical disks drives and presents them to a server as logical units, and forms the interface to a storage area network for server access. The term disk in this context is synonymous with a hard disk drive (HDD), a direct access storage device (DASD) or a logical unit number (LUN) in a storage device. Unless the context indicates otherwise, the term “disk” as used herein is intended to embrace not only magnetic storage devices, but also optical, solid state and other types of storage devices.
A storage area network (SAN) is an architecture to attach remote storage devices to servers in such a way that the storage devices appear as locally attached to the operating system. Network Attached Storage (NAS), in contrast to SAN, uses file-based protocols where it is clear that the storage devices are remote.